docs: def _get_seqprop_to_structprop_alignment(self, seqprop, structprop, chain_id):
          """Return the alignment stored in self.sequence_alignments given a seqprop, structuprop, and chain_id"""
          full_structure_id = '{}-{}'.format(structprop.id, chain_id)
          aln_id = '{}_{}'.format(seqprop.id, full_structure_id)
  
          if self.sequence_alignments.has_id(aln_id):
              alignment = self.sequence_alignments.get_by_id(aln_id)
              return alignment
          else:
              raise ValueError('{}: structure alignment not found, please run the alignment first'.format(aln_id))